Organic Chemistry Chapter 12 Organic Chemistry Organic chemistry

Organic Chemistry Chapter 12

Organic Chemistry • Organic chemistry: the study of the compounds of carbon – organic compounds are made up of carbon and only a few other elements – chief among these are hydrogen, oxygen, and nitrogen – also present are sulfur, phosphorus, and a halogen (fluorine, chlorine, bromine, or iodine)

Organic Chemistry – the experiment of Wöhler in 1828 was the first in a series of experiments that led to the demise of the vital force theory

Organic Chemistry • The link to biochemistry – carbohydrates, lipids, proteins, enzymes, nucleic acids, hormones, vitamins, and almost all other chemicals in living systems are organic compounds

Organic Structure – Make a model of each of these structures:

Organic Structure – VSEPR model: the most common bond angles are 109. 5°, 120°, and 180°

Functional Groups • Functional group: anything other than just C-C, or C-H bonds! • Functional groups are important because – they undergo the same types of chemical reactions no matter in which molecule they are found – to a large measure they determine the chemical and physical properties of a molecule – Naming is based on FG.

Functional Groups • Five important functional groups

Chapter 11 Alkanes and Cycloalkanes

Alkanes • Alkanes: hydrocarbons containing only carbon-carbon single bonds – the first two alkanes are methane and ethane

Alkanes • line-angle formula: – a line represents a carbon-carbon bond an angle represents a carbon atom – a line ending in space represents a -CH 3 group – hydrogen atoms are not shown in line-angle formulas

Alkanes – the first 10 alkanes with unbranched chains

Constitutional Isomerism • Constitutional isomers: compounds that have the same molecular formula but different structural formulas – for the molecular formulas CH 4, C 2 H 6, and C 3 H 8, only one structural formula is possible. – for the molecular formula C 4 H 10, two constitutional isomers are possible

Constitutional Isomerism – Problem: do the structural formulas in each set represent the same compound or constitutional isomers?

Constitutional Isomerism – Solution: (a) they represent the same compound – Solution: (b) they represent constitutional isomers

Constitutional Isomerism – Problem: draw structural formulas for the five constitutional isomers of molecular formula C 6 H 14

Constitutional Isomerism – Problem: draw structural formulas for the five constitutional isomers of molecular formula C 6 H 14 – Solution:

IUPAC Names • The IUPAC name of an alkane with an unbranched chain of carbon atoms consists of two parts: – (1) a prefix: the number of carbon atoms in the chain – (2) the suffix -ane: -ane shows that the compound is a saturated hydrocarbon

IUPAC Names • The name of an alkane with a branched chain of carbon atom consists of – a parent name: the longest chain of carbon atoms – substituent names: the groups bonded to the parent chain

IUPAC Names • Alkyl group: a substituent group – named by dropping the -ane from the name of the parent alkane and adding the suffix -yl

IUPAC Names-Review 1. The name for an alkane with an unbranched chain of carbon atoms consists of a prefix showing the number of carbon atoms and the ending -ane 2. For branched-chain alkanes, longest chain of carbon atoms is the parent chain 3. Name and number each substituent on the parent chain; use a hyphen to connect the number to the name

IUPAC Names-Details 4. If there is one substituent, number the parent chain from the end that gives the substituent the lower number

IUPAC Names-Details 5. If the same substituent occurs more than once, – indicate the number of times the substituent occurs by a prefix di-, tri-, tetra-, penta-, hexa-, and so on – use a comma to separate position numbers

IUPAC Names- Details 6. If there are two or more different substituents – list them in alphabetical order – number the chain from the end that gives the lower number to the substituent encountered first – if numbering is the same in both directions, give the substituent of lower alphabetical order the lower number

IUPAC Names-Details 7. Do not include the prefixes di-, tri-, tetra-, and so on, or the hyphenated prefixes sec- and tert- in alphabetizing; – alphabetize the names of substituents first, and then insert these prefixes

Common Names • Common names- older system – use the IUPAC system for our class!

Cycloalkanes Alkanes whose carbon atoms are joined in rings are called cycloalkanes. They have the general formula Cn. H 2 n where n = 3, 4, … 24. 2

Cycloalkanes • Cyclic hydrocarbon: a hydrocarbon that contains carbon atoms joined to form a ring • Cycloalkane: a cyclic hydrocarbon in which all carbons of the ring are saturated – cycloalkanes of ring sizes ranging from 3 to over 30 carbon atoms are found in nature – five-membered (cyclopentane) and six-membered (cyclohexane) rings are especially abundant in nature

Cycloalkanes • Nomenclature – Prefix cyclo-, – if only one substituent, no location number – if there are two substituents, number the ring beginning with the substituent of lower alphabetical order.

Name These Cycloalkanes

Conformations - Alkanes – Molecules move a lot … each movement result in a different conformation … each conformation has an associated energy … some conformations are more stable than others! – following are three conformations for a butane molecule

Cyclopropane Hydrogen's move to alleviate eclipsing energies

Cyclobutane

Cyclopentane

Cyclopentane • The most stable conformation of a cyclopentane ring is an envelope conformation

Cyclohexane

Cyclohexane • The most stable conformation of a cyclohexane ring is the chair conformation – all bond angles are approximately 109. 5°

Cyclohexane • In a chair conformation, – six C-H bonds are equatorial – six C-H bonds are axial

Draw the Chair

Cyclohexane – the more stable conformation of a substituted cyclohexane ring has substituent group(s) equatorial rather than axial

Axial vs. Equatorial Which is more stable?

Cycloalkanes cis and trans H 3 C CH 3 cis-1, 2 -dimethylcyclopropane H 3 C CH 3 cis-1, 2 -dimthylcyclobutane CH 3 trans-1, 2 -dimethylcyclopropane trans-1, 2 -dimthylcyclobutane If a ring has two substituents on it, they can be on the same side (cis) or the opposite side (trans).

Cis-Trans Isomers – alternatively, we can view it from above

Cis-Trans Isomers – to determine cis-trans isomers if cis-trans isomers are possible, we can view a cyclohexane ring as a planar hexagon – because cis-trans isomers differ in the orientation of their atoms in space, they are stereoisomers – cis-trans isomers are one type of stereoisomers

Alkane Nomenclature-Review 1. Find the longest continuous chain of carbon atoms in the molecule. This is the “parent” name. … or the ring is the parent. 2. Branched are named as an alkyl group. 3. Substituents are numbered in the direction that gives the smaller numbers for the locations of the branches. 4. Use prefixes di-, tri-, tetra-, when there is more than one alkyl branch of the same kind. 5. Use previous rules for other types of substituents. Write them in alphabetical order. 24. 2

What is the IUPAC name of the following compound? CH 3 1 CH 2 C 2 H 5 CH 2 3 CH 4 CH 2 5 CH 2 6 CH 2 7 CH 3 8 4 -ethyl-2 -methyloctane What is the structure of 2 -ethyl-4 -methylhexane? Can you name it properly? C 2 H 5 CH 3 1 CH 2 3 CH 4 CH 2 5 CH 3 6 True Name: 3, 5 -dimethlyheptane 24. 2

Alkane Chemistry Key reactions: 1) Burning • CH 4 + O 2 ® CO 2 + H 20 + Heat 2) Chlorination • CH 3 + Cl 2 ® CH 3 CH 2 Cl + HCl • Note that multiple chlorination reactions can occur in uncontrolled environments.

Monochlorinate Butane 1) When butane is chlorinated, the C 1 and C 2 products are different. 2 structural isomers * • A chiral carbon • See CH 15

Formation of 2 -chlorobutane

Mechanism of formation Planer Intermediate Both mirror images 0 ptically different